an email to M-audio tech support

David French

Well-Known Member
Joined
Jun 19, 2002
Location
Indiana
What's going on here?!? I am having some odd signal level problems for which I have no explanation. I have sent an email to M-Audio's tech support department :roll: . I don't expect them to be able to help me so I thought I'd ask the more educated RO community. All the details of this problem are in the quote below. Thanks in advance.

I recently purchased a Sytek MPX-4a solid state mic pre to provide pres
for channels three and four of my Delta 66. I am connecting the Sytek via
line ins three and four of the Omni I/O. Since the manual for the Omni I/O states that the 1/4" jacks on line ins three and four will accept
either TS for unbalanced operation or TRS for balanced operation, I chose to use FXLR to 1/4" TRS balanced cables (in the standard pin 1 GND, pin 2 POS, pin 3 NEG : tip POS, ring NEG, shield GND configuration) for a balanced connection. The results were surprising. The Sytek pre can supply up to 72 dB of gain, compared the the 66 dB supplied by the Omni's pres, yet while amplifying the output of my R0DE NTK mic, an 11 o'clock position on the Omni's preamp one gain knob produces a similar signal level as the Sytek cranked to its highest setting. Something is obviously wrong here, and no, it's not with my preamp or my cables. I started my own investigation into this matter by custom fabbing a cable in order to see how things went when I chose an unbalanced configuration. This cable is wired such that pins 1 and 3 of an XLR connector are jointly conected to the shield of an unbalanced cable and pin 2 is conected to the positive lead. I can do this because the Sytek's output is servo balanced (cross-coupled) to allow for unbalanced operation. I performed an experiment by recording a standardized input from a tone generator first with the balanced cable and second with the unbalanced cable. During both recordings, the gain on the Sytek was not changed and neither was the input selector on the software control panel, which was set to -10 dB. I found that the tone recorded with the unbalanced cable was about 7 dB louder. Can you please help me find out why I cannot achieve a higher signal level with my Sytek in a balanced configuration? Thank you.
 
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